1. Technical Field
The present disclosure relates generally to the treatment of respiratory conditions with continuous positive airway pressure (CPAP) devices, and more particularly, to auto-titration of prescription pressure to improve comfort for patients beginning CPAP therapy.
2. Related Art
Sleep apnea is a serious medical condition in which patient breathing during sleep pauses abnormally, or is abnormally low. Apnea is categorized as obstructive, central, and combined obstructive and central, though the obstructive sleep apnea (OSA) is the most common. The patient's upper airway repeatedly narrows or collapses, causing pauses in breathing that may extend in duration up to half a minute. Although some degree of apnea is considered normal, in more severe cases, daytime sleepiness and fatigue may result as a consequence of reduced blood oxygen saturation, as well as constant interruptions to sleep cycles resulting from patients gasping for air. There have been studies linking sleep apnea to more severe long-term health issues including heart disease and depression, and recently, to cancer as well. With apnea being strongly linked to obesity, and with obesity being projected to increase, the number of patients suffering from sleep apnea is likely to increase concomitantly.
One common treatment for obstructive sleep apnea is continuous positive airway pressure (CPAP) therapy, where a positive pressure is applied to the patient to prevent its collapse as would otherwise occur during an apnea episode. By retaining the patient's airway, normal, uninterrupted breathing during sleep is ensured. In a basic implementation, CPAP therapy applies a constant pressure that is not tied to the patient's normal breathing cycle. The positive airway pressure is desired in the inspiratory phase when the pressure differences between the lungs and the nose contribute to the collapse of the intermediate airway. Earlier patient breathing assistance devices tended to be uncomfortable to use because of the bulkiness associated with the patient interface, as well as the misapplication of pressure resulting from sub-optimal control methodologies. Various improvements have been developed to reduce discomfort during therapy, particularly at critical points along the patient's respiratory cycle. Thus, what was previously prescribed only for the more severe cases of sleep apnea in which the benefits of treatment outweighed the significant discomfort is now useful for treating a wider spectrum of sleep apnea conditions.
Although a properly set therapeutic pressure level alleviates apnea and hypopnea conditions, a determination of the required pressure balanced against the comfort demands of the patient may involve complicated diagnostics and/or several sleep cycles of trial-and-error adjustments. As a general matter, the application of pressure against the respiratory efforts of the patient and consequent increase in work of breathing may induce a sense of asphyxiation, so any excess therapeutic pressure causes needless discomfort.
Conventionally, most patients begin CPAP treatment following a diagnostic test at a sleep lab. Such sleep studies are understood to involve the measurement of several sleep indicators including an apnea and hypopnea index (AHI). When the AHI exceeds a threshold value more than five times an hour, that patient is deemed to be suffering from obstructive sleep apnea and hence in need of treatment. The following night, the patient is scheduled for titration, which also takes place in the sleep lab, and involves attempting the reduction of the AHI to less than five events per hour by increasing pressure. Pressure increases are typically applied when the patient is in a sleep state, and thereby avoiding the aforementioned feeling of asphyxiation that may otherwise occur as a result of pressure against breathing efforts in a wakeful state.
After titration, the patient is prescribed a CPAP device for home use. During initial treatment, because of the unfamiliar sensations that the patient may experience as a result of the applied airway pressure, there may be significant discomfort. This discomfort may be so severe that the patient detrimentally stops treatment. In response, the medical practitioner may prescribe a bi-level device that improves comfort and reduces the feelings of asphyxiation, particularly during the wakeful states. Bi-level devices are understood to apply two different pressure levels depending on the respiratory phase—higher pressures during inspiration, and lower pressures during exhalation. Thus, in summary, a typical patient suffering from sleep apnea/hypopnea first undergoes a diagnostic step, followed by a titration step in the sleep lab, followed by a trial step of using the CPAP device and experiencing discomfort, and a treatment modification step to change to a bi-level device to assist with compliance.
Alternatively, the sleep study may be omitted and instead substituted with a home-use diagnostic device in the interest of cost reduction in the diagnosis and treatment of sleep apnea/hypopnea. The diagnostic device is used on a single night, and returned to a laboratory where the results are analyzed. The turnaround for this service may be a few days, and if apnea/hypopnea is detected in the patient, e.g., the calculated AHI is greater than 5 per hour, the patient may be provided with an automatically titrating CPAP device. The typical protocol is to start pressure at low levels, for example, 4 cm H2O, and in response to the patient experiencing apneic events, gradually increasing pressure on an event-by-event basis to reach a therapeutic pressure.
There are several disadvantages associated with such automatic titration, also referred to in the art as auto-CPAP. One issue is that the patient is under-titrated on any given night because the increase in pressure is in response to an apnea event. Thus, there is discomfort and sleeplessness associated with being aroused awake because of the apnea/hypopnea condition, possibly over an extended duration. In other words, the therapeutic effects of using the CPAP device may be minimal. Another issue is that the titration is set most suitably for apneas and hypopneas, and does not account for the discomfort associated with ariophagia (air entering the stomach) or over-titration that may not account for central apnea. Conventional titration techniques tend to disregard patient comfort and instead operate under the expectation that the patient will eventually become accustomed. However, this expectation tends to have the opposite effect of discouraging treatment compliance.
Accordingly, there is a need in the art for improved CPAP automatic titration that transitions the patient from a minimized, comfortable level to full prescription level while maintaining comfortable pressure levels at any given point in treatment, including the initial phases when the patient is becoming accustomed to the resistance against constant pressure. There is also a need in the art for minimizing AHI despite the presence of untreatable central apnea without over-titration.